Heat places a strain on the body and leads to an increased risk of healthcare use and death among vulnerable or overexposed populations. These increased risks, which are particularly pronounced when heat is unusual, intense, and prolonged, can result in very high excess mortality and strain on healthcare systems. The interministerial heat wave directive, coordinated by the Ministry of Health, has been implemented every summer since 2004 to manage these unusual situations. It is in effect from June 1 to September 15. Within this framework, Santé publique France is responsible for: monitoring the health impact during heat wave alerts via the Heat Wave and Health Alert System (SACS), to complement the meteorological monitoring conducted by Météo-France; and preventing the individual health effects of heat through a prevention and communication strategy implemented before and during heat wave alerts. This document explains what a heat wave is, its health risks, and the people most at risk; it also presents the alert and monitoring system and the public health prevention measures implemented by Santé publique France in this area.